1. Field of the Invention
The present invention relates to a waste water treatment method and apparatus for collecting sludge, oily substances, scum, and so on which exist in waste water, float and precipitate therein and for reducing the volume thereof by dehydrating them.
2. Description of the Related Art
Conventionally, waste water, which was discharged from kitchens, meat and marine product processing factories, oil manufacturing factories, oil and fat processing factories, repair shops, gas stations, and the like, included a large amount of wastes which contained animal oils and fats, vegetable oils and mineral oils, and wastes containing animal and vegetable oily substances which were made when various materials were processed.
Since these wastes must be previously removed from the waste water when the waste water is treated, they were conventionally separated and removed with nets, screen meshes and the like. However, when the waste water contains oily substances, they float in the waste water or on the surface thereof as grease-like lumps containing water and sludge or as scum-like lumps containing bubbles.
When the waste water is to be purified, it is an important theme to subject the waste water to biological treatment to permit a prescribed quantity of microorganisms to live in the waste water.
Microorganisms in water have a self-purifying capability. When, however, the amount of oxygen supplied into the water is smaller than the amount of oxygen consumed by them, aerobic microorganisms, which live by taking oxygen, will die because the amount of oxygen dissolved in water is reduced. When no oxygen exist in the water, anaerobic microorganisms, which take oxygen contained in organic matters, will breed and reduce and decompose the organic matters.
The biological treatment is classified into an aerobic treatment and an anaerobic treatment: in the aerobic treatment, oxygen contained in air is sufficiently supplied to polluted water by aeration and the like so that dirt is decomposed and purified; whereas, in the anaerobic treatment, air is prevented from being in contact with polluted water so that anaerobic organisms breed in the area where no oxygen exists and decompose and purify the dirt.
However, since the waste water from kitchens and the like contains a large amount of suspended oily substances, the waste water has a problem that oil sludge clings to a fluidized bed, that is, to the surfaces of carriers onto which microorganisms cling and chokes the microorganisms clinging onto the carriers when the biological treatment is performed.
Since the waste water containing the oily substances clogs nets, screen meshes and the like, the oily substances cannot be separated and removed. The animal oils and fats contained in waste water discharged from kitchens and the like are not solidified while they are at a high temperature. However, since they are solidified when cooled in such places as a raw water tank for treating waste water, a cesspool located at some midway point and a watercourse, the flow of the waste water is obstructed by the solidified animal oils and fats and cannot be treated well.
To remove scum and the like clinging to the tank and the like, there was conventionally employed a method of heating the portions of them which are liable to precipitate by steam or hot water piping. However, the scum and the like which contain sludge and residues, become creamy or sometimes contain bubbles have a problem that they cannot be removed even if they are heated as well as they are removed in only a limited amount even if a worker remove them with a rod or a ladle. Thus, there arises a problem that raw water tanks for treating waste water, cesspools located at some midway point and the like are made unusable.